An endoscope is widely used to examine and care portions of a human's body such as duodenum, rectum, large intestine, oesophagus, ears, nose, and urinary bladder.
An electronic endoscope has been recently constructed as follows. Namely, the electronic endoscope comprises, in the front to back direction thereof, an end tip portion for disposing therein a solid image pick-up element (the CCD in the following description) and an optical system for observing a body, a bent portion moved in the upward, downward, right and left directions by the operation of an operator, a guide portion for disposing therein a light guide, a signal line, and a scope portion composed of a hand operating portion, etc. The light from a light source lamp is collected by a collecting mirror and a condenser lens, and is then guided to the light guide composed of optical fibers.
When the quantity of light transmitted to the light guide is too large, halation or blooming occurs to an observed region of the observed body provided by the CCD. When the quantity of light is too small, it is difficult to sufficiently secure the visual field. Accordingly, in the operation of the endoscope, it is necessary to suitably control the quantity of light transmitted to the light guide from the light source apparatus.
In the conventional light source apparatus of the endoscope, a control apparatus illustrated in FIGS. 1A, 1B, 2A and 2B is used as a means for controlling the illuminating intensity.
Namely, in a conventional apparatus shown in FIGS. 1A and 1B, two light interrupting plates A and B are disposed between a condenser lens 3 and a rear end surface 42 of a light guide 4, and are slid in the direction of arrow a with respect to a light flux 44, thereby adjusting the quantity of the incident light irradiated to the light guide 4.
In a conventional apparatus shown in FIGS. 2A and 2B, a light interrupting plate C having a generally Y shape is disposed between the condenser lens 3 and the rear end surface 42 of the light guide 4, and is slid in the direction of arrow b with respect to the light flux 44, thereby adjusting the quantity of the incident light irradiated to the light guide 4.
In the above-mentioned conventional apparatuses shown in FIGS. 1A, 1B, 2A and 2B, the light quantity is adjusted by reducing the collected light flux from the peripheral portion thereof between the condenser lens 3 and the light guide 4 using the light interrupting plates A, B and C. Accordingly, although it is possible to control the illuminating intensity by the nature of the light guide by which light is irradiated only in the same direction as the incident angle, the light distributing characteristics or the intensity distribution of the light irradiated to the illuminated body from the other end of the light guide is changed in accordance with the reduction of the light flux so that a suitable light quantity cannot be obtained in some portions in the visually observed field.